Resistance change memory is known as a type of a semiconductor memory device. As a type of resistance change memory, MRAM (magnetoresistive random access memory) is known. MRAM is characterized by its high-speed operation, large capacity, and non-volatility. MRAM is viewed as a next-generation memory device that replaces volatile memory such as DRAM and SRAM, and much effort has been made to research and develop MRAM.
For MRAM, magnetoresistive elements utilizing a TMR (tunneling magnetoresistive) effect are used as memory cells that store information. As magnetoresistive elements, MTJ (magnetic tunnel junction) elements are used which have a stack of a metal magnetic film/an insulating film/a metal magnetic film. A change in the resistance of the MTJ element depends on a magnetization state of the metal magnetic films which sandwich the insulating film therebetween. In other words, MRAM stores data depending on the magnetization state of the MTJ element.
As MRAM is increasingly miniaturized, the distance between adjacent MTJ elements decreases. Therefore, the characteristics of the adjacent MTJ elements are degraded or vary under the effect of stray fields. Thus, to achieve a high data holding characteristic and to reduce inappropriate operations, MRAM needs to be improved to reduce the adverse effects of stray fields from the MTJ elements.